Information technology (IT) environments featuring virtualized server, network and storage infrastructure are becoming increasingly commonplace due to the cost savings that can be obtained through reducing the amount of physical hardware needed to provide IT, network and storage services. Furthermore, cloud-based services are becoming increasingly attractive as they reduce the need to deploy and procure physical hardware, Operational Support Systems (OSS) and other systems whilst allowing consumers to adopt a “compute-on-demand” model of operation.
Virtualization technologies, such as VMware with VMotion (VMware and VMotion are trade marks of VMware, Inc.), allow virtualized resources to be moved across hosts and enabled/disabled at-will or in response to observed system metrics, such as central processing unit (CPU) load. To support these environments, cloud computing providers and operators usually use a variety of software tools to support the typical FCAPS (fault, configuration, accounting, performance, security) activities required to provision, measure and troubleshoot virtualized services and their underlying physical infrastructure. Some cloud computing providers may also offer their customers self-service portals which complicates the management process due to the unpredictable nature of compute-on-demand. Similarly, application placement, whether deployed to physical or virtualized servers and storage, is key to providing high quality services.
Service quality can be measured in numerous ways but one key factor in any measurement is the time taken, or network latency, for components of a composite service to communicate with each other. The overall network latency between networked components has many factors such as queuing delays, protocol delays and propagation delays.
Propagation delay varies depending on network medium and the physical distance between networked components. For example, in a glass fibre optic cable used to carry data, the speed of light (c) in the physical medium (s) is slowed down because it is not travelling through a vacuum and this is as a result of the refractive index of the network medium (n). For example, if the refractive index of a given fibre optic cable is 1.51, then the speed of light through it is given by:
Let c = 299,792,458 m/s// speed of light in a vacuumLet s = c = 299,792,458 m/s =// speed of light in198,538,051.65 m/s// n 1.51//the medium (~66% of c)
Then, using standard time-distance calculations, the theoretical propagation delay time can be calculated. For example, if the distance between London and New York is approximately 5,576 km, then the propagation delay time is approximately:
Let t=d=5,576,000 m=˜0.028 seconds or 28 ms.
s=198,538,051.65 m/s